1. Field of Invention
The present invention, which belongs to a field of microwave source technology, relates to a microwave power source, and more particularly to an injection locked magnetron microwave generator.
2. Description of Related Arts
The microwaves are widely applied in the fields of radar, communication, microwave power transmission and microwave heating. Along with the development of economy and technology, the microwave energy is applied in more and more fields. The devices for generating microwaves are generally divided into the solid state devices and the vacuum tubes. The vacuum tubes generally have a high direct current to microwave conversion efficiency, and especially the magnetron, which belongs to the vacuum tube, has a low cost and a high power-mass ratio.
Despite of the high conversion efficiency, the magnetron usually has an extremely poor output characteristic that the output frequency and the output phase vary randomly, and thus becomes a microwave generator without a good output characteristic. The injection locking technology is able to improve the output characteristic of the magnetron, wherein a frequency of an output signal of the magnetron is controlled by a frequency of an external injection signal; and a fixed phase difference exists between a phase of the output signal and a phase of the external injection signal. A conventional injection locked magnetron system, as showed in FIG. 1, comprises a magnetron, a microwave source and a locking device. An accurate injection signal (a locking signal) with a stable frequency, generated by the microwave source, is injected into the magnetron through the locking device, for locking the magnetron. Due to the high parameter requirement upon the locking signal outputted by the microwave source, the microwave source usually has a complex structure. When an output power of the magnetron reaches 1 kW level, the injection locking requires an injection signal with high power, which leads to a high cost. Considering the cost, an injection signal with low power is injected into the magnetron to realize the injection locking, so as to reduce the cost of the microwave source and the cost of the overall microwave generator. The injection of the injection signal with the low power into the magnetron results in the multiple output frequencies of the magnetron, rather than a dot frequency. The magnetron has power outputting in a frequency band, wherein merely the microwave signal at a certain frequency is useful and the microwave signals at other frequencies are all useless, also called spurious microwave signals. It is failed to effectively lock the output signal of the magnetron and the spurious microwave signals are outputted, which reduces the useful power outputted by the magnetron and degrades the microwave conversion efficiency of the magnetron.